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Sep 21, 2013
09/13

by
Andrew Randono; David Sloan

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In this paper we investigate the manner in which the internal spin angular momentum of a spinor field is encoded in the gravitational field at asymptotic infinity. The inclusion of internal spin requires us to re-analyze our notion of asymptotic flatness. In particular, the Poincar\'{e} symmetry at asymptotic infinity must replaced by a spin-enlarged Poincar\'{e} symmetry. Likewise, the generators of the asymptotic symmetry group must be supplemented to account for the internal spin. In the...

Source: http://arxiv.org/abs/0905.4529v2

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Jul 20, 2013
07/13

by
Julian Rennert; David Sloan

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We examine spinfoam cosmology by use of a simple graph adapted to homogeneous cosmological models. We calculate dynamics in the isotropic limit, and provide the framework for the aniostropic case. The dynamical behaviour is calculating transition amplitudes between holomorphic coherent states on a single node graph. The resultant dynamics is peaked on solutions which have no support on the zero volume state, indicating that big bang type singularities are avoided within such models.

Source: http://arxiv.org/abs/1304.6688v1

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Sep 22, 2013
09/13

by
Abhay Ashtekar; David Sloan

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Inflationary models of the early universe provide a natural mechanism for the formation of large scale structure. This success brings to forefront the question of naturalness: Does a sufficiently long slow roll inflation occur generically or does it require a careful fine tuning of initial parameters? In recent years there has been considerable controversy on this issue. In particular, for a quadratic potential, Kofman, Linde and Mukhanov have argued that the probability of inflation with at...

Source: http://arxiv.org/abs/1103.2475v1

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Sep 21, 2013
09/13

by
Abhay Ashtekar; David Sloan

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We consider $d>4$-dimensional space-times which are asymptotically flat at spatial infinity and show that, in the first order framework, the action principle is well-defined \emph{without the need of infinite counter terms.} It naturally leads to a covariant phase space in which the Hamiltonians generating asymptotic symmetries provide the total energy-momentum and angular momentum of the isolated system. This work runs parallel to our previous analysis in four dimensions \cite{aes}. The...

Source: http://arxiv.org/abs/0808.2069v1

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Sep 23, 2013
09/13

by
Tomas Liko; David Sloan

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We show that the on-shell path integral for asymptotically flat Euclidean spacetimes can be given in the first-order formulation of general relativity, without assuming the boundary to be isometrically embedded in Euclidean space and without adding infinite counter-terms. For illustrative examples of our approach, we evaluate the first-order action for the four-dimensional Euclidean Schwarzschild and NUT-charged spacetimes to derive the corresponding on-shell partition functions, and show that...

Source: http://arxiv.org/abs/0810.0297v4

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Sep 17, 2013
09/13

by
Abhay Ashtekar; David Sloan

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In loop quantum cosmology (LQC) the big bang is replaced by a quantum bounce which is followed by a robust phase of super-inflation. Rather than growing unboundedly in the past, the Hubble parameter \emph{vanishes} at the bounce and attains a \emph{finite universal maximum} at the end of super-inflation. These novel features lead to an unforeseen implication: in presence of suitable potentials all LQC dynamical trajectories are funneled to conditions which virtually guarantee slow roll...

Source: http://arxiv.org/abs/0912.4093v2

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Jul 20, 2013
07/13

by
John D. Barrow; David Sloan

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We examine the evolution of a closed, homogeneous and anisotropic cosmology subject to a variation of the fine structure 'constant', \alpha, within the context of the theory introduced by Bekenstein, Sandvik, Barrow and Magueijo, which generalises Maxwell's equations and general relativity. The variation of \alpha permits an effective ghost scalar field, whose negative energy density becomes dominant at small length scales, leading to a bouncing cosmology. A thermodynamically motivated coupling...

Source: http://arxiv.org/abs/1304.6699v1

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Sep 20, 2013
09/13

by
Abhay Ashtekar; Jonathan Engle; David Sloan

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We consider 4-dimensional space-times which are asymptotically flat at spatial infinity and show that, in the first order framework, action principle for general relativity is well-defined \emph{without the need of infinite counter terms.} It naturally leads to a covariant phase space in which the Hamiltonians generating asymptotic symmetries provide the total energy-momentum and angular momentum of the space-time. We address the subtle but important problems that arise because of logarithmic...

Source: http://arxiv.org/abs/0802.2527v2

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Sep 18, 2013
09/13

by
Abhay Ashtekar; Adam Henderson; David Sloan

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The Belinskii, Khalatnikov and Lifshitz conjecture \cite{bkl1} posits that on approach to a space-like singularity in general relativity the dynamics are well approximated by `ignoring spatial derivatives in favor of time derivatives.' In \cite{ahs1} we examined this idea from within a Hamiltonian framework and provided a new formulation of the conjecture in terms of variables well suited to loop quantum gravity. We now present the details of the analytical part of that investigation. While our...

Source: http://arxiv.org/abs/1102.3474v2

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Sep 22, 2013
09/13

by
Abhay Ashtekar; Adam Henderson; David Sloan

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The Belinkskii, Khalatnikov and Lifshitz conjecture says that as one approaches space-like singularities in general relativity, 'time derivatives dominate over spatial derivatives' so that the dynamics at any spatial point is well captured by an ordinary differential equation. By now considerable evidence has accumulated in favor of these ideas. Starting with a Hamiltonian framework, we provide a formulation of this conjecture in terms of variables that are tailored to non-perturbative...

Source: http://arxiv.org/abs/0811.4160v2

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Oct 24, 2014
10/14

by
Ichinose, Genki; Saito, Masaya; Sayama, Hiroki; Wilson, David Sloan

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This article is from Scientific Reports , volume 3 . Abstract Migration is a fundamental trait in humans and animals. Recent studies investigated the effect of migration on the evolution of cooperation, showing that contingent migration favors cooperation in spatial structures. In those studies, only local migration to immediate neighbors was considered, while long-range migration has not been considered yet, partly because the long-range migration has been generally regarded as harmful for...

Source: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3752612